Production of unsaturated dimers of alpha alkyl styrenes



, Patented a. 28, 1941 um'rlai) STATES PATIENT OFFICE.

PRODUCTION OF UNSATURATED DIMERS OF ALPHA ALKYL STYRENES Arthur B. Hersberger, Drexel Hill, and Randall G. Heiligmann, Yeadon, Pa., assignors to The Atlantic Refining Company, Philadelphia, Pa., a corporation of Pennsylvania No Drawing.

A plication January is, 1946, Serial No. 642,100

Claims. (01. 260-669) The present invention relates to the production wherein X may be an alkyl group such as methyl, ethyl, propyl, or isopropyl, but is preferably methyl, and Y may be hydrogen or alkyl,- cycloalkyl, aryl, substituted aryl, or cycloalkenyl group, but is preferably hydrogen or methyl, ethyl, propyl, or isopropyl.

We have found that substantial yields of unsaturated dimers relatively free of cyclic saturated dimers may be obtained by treating a monomeric alpha alkyl styrene, such as alpha methyl styrene, with a catalyst comprising sulfuric acid of certain concentrations under controlled temperature conditions. More specifically, we have found that the unsaturated dimers, substantially free of cyclic saturated dimers, may be produced by intimately contacting an alpha alkyl styrene with sulfuric acid of 30% to 65% concentration at temperatures between 150 F. and 220 F., and preferably between-170 F, and 200 F. We have further found that similar results may be obtained using sulfuric acid of to concentration at temperatures between 60 F. and 220 F., and preferably between F. and F. The use ofsulfuric acid of concentrations below about 50% at temperatures below about 150 F. gives relatively poor yields of unsaturated dimer, while the use of sulfuric acid of concentrations above about 65% at ordinary temperatures (60 F.- F.) gives substantial conversion to undesirable cyclic saturated dimers, and at elevated temperatures F. to 220 F.) gives almost complete conversion to the saturated'dimer. The presence of the cyclic saturated dimer as a contaminant in the unsaturated dimer is undesirable in many in-' stances, and once formed is very diflicult if not impossible to remove since its boiling point is very close to that of the unsaturated dimer. It is therefore an object of this invention to produce the unsaturated dimer to the substantial exclusion of the cyclic saturated compound.

In carrying out our process, the alpha alkyl styrene is introduced into a suitable vessel provided with means for controlling the temperature, such as a jacket or internal tubes for circulating a heat exchange medium, and the required quantity of sulfuric acid of proper concentration is added, the entire mixture being thoroughly'agitated by mechanical or other means during the ensuing polymerization reaction. The quantity of acid used may range from 0.5 to. 5 volumes per volume of monomeric alpha alkyl styrene, and in general a ratio of 3 to 1 or 4 to 1 is satisfactory. The con- 'version time required is dependent to some extent upon the quantity and concentration of the sulfuric. acid catalyst, as well as upon the temperature of reaction. 'Eflicient conversions have been obtained in from 2 to 8 hours, although shorter or longer periods may be required in some cases. When sulfuric acid of 50% to 65% concentration is used, the reaction temperature may range from 60 F. to 220 F., and with acid concentrations of 30% to 65%, a temperature of 150 F. to 220 F. may be used. Low concentrations of acids, 1. e., 30%-40%, for example, 'are not particularly effective at temperatures below'about 150 F. Upon completion of the treatment of the monomeric alpha alkyl styrene with the sulfuric acid catalyst to effect conversion thereof to the unsaturated dimer relatively free of cyclic saturated dimer, the reaction mixture is permitted to settle and stratify, the lower layer of sulfuric acid thereafter being separated from the upper hydrocarbon layer. The upper layer may be neutralized with a solution of a base, if necessary, or may besimply water washed to remove traces of entrained acid. Such upper layer may then be fractionally distilled, preferably under reduced pressure, to separate unconverted monomer, unsaturated dimer, and small amounts of higher polymers which may be formed as by products. Careful control of the polymerization conditions minimizes the formation of these higher polymers, and since the boiling point thereof is substantially higher than that of the desired. unsaturated dimer, such higher polymers are amenable to separation by fractionation. If desired, the conversion reaction may be carried out continuously by passing the monomeric alpha alkyl styrene, in a fine state of dispersion, countercurrent to a stream of the acid catalyst, provision being made a to separate and recycle any unconverted mono- 'meric alkyl styrene for further treatment. Catalyst activators such as metal salts, for example, mercuric sulfate, may be incorporated in smallamounts in the sulfuric acid to enhance the activity thereof.

Our invention may be furtherillustrated by the following examples, which, however, are not to I be construed as limiting the scope thereof.

Monomeric alpha methyl styrene was intimate- 1y contacted with various concentrations ofsulfuric acid at different temperatures, and the reaction mixture was then separated,the sulfuric.

Sulfuric Acid Reaction Per Cent Per Cent Per Cent Unoon- Unsat. Sat.

Concen- Quan- Temp., Time, verted dimer dimer tration tity F. hrs.

Per cent Per cent 1 30 400 170-190 4 60 40 40 400 170-190 4 57 43 0 50 400 122-180 6 0 99 l 60 400 122-180 6 0 98 2 60 3 150-180 6 88 12 0 60 6 150-180 6 80 20 0 60 100 150-180 6 23 75 2 70 400 180-190 6 0 10 90 so 400 70- 80 s so 20 0 60 400 70- 80 8 0 100 0, 70 400 75-100 8 0 90 10 80 400 75-100 0 a 0 100 In the above examples, the determination or the quantities of the unsaturated dimer and the cyclic saturated dimer were made by means of unsaturated dimer had a boiling point'of 243 lat-248 F. at 0.1 mm. pressure, a refractive indexof 1.5677 at 20 C., and a bromine number of 67. The cyclic saturated dimer had a boiling point of 244 LEE-248 F., a refractive index of- 1.5633 at 20 C., a bromine number of 0, and a melting point of 126 F.-129 F. I

From the above examples it is evident that the use of sulfuric acid catalyst in concentrationsof 70% or higher produced undesirably large quantitles of the cyclic saturated dimer. It is there- 4 fore an object of this invention to utilize sulfuric acid catalysts having a concentration below that at which substantial amounts of the-cyclic saturated dimer are produced, i. e., concentrations not greater than about 65%,.whereby there may be produced an unsaturated dimer having a low content of saturated dimer.

' While the present invention has been described particularly with reference to the dimerization of the alpha methyl styrene, such invention is equally well adapted in the polymerization ofother alpha allwl styrenes or'mixtures' thereof, including but not limited to alpha methyl para methyl 55 styrene, alpha methyl para ethyl styrene, alpha methyl para propyl styrene, alpha methyl para isopropyl styrene, alpha methyl meta methyl styrene, alpha ethyl styrene, alpha ethyl para ethyl styrene, alpha propyl styrene, alpha propyl para propyl styrene, and the like.

We claim: 1. A process for producing v the unsaturateddimer of an alpha alkyl styrene, which comprises intimately contacting said alpha alkyl styrene 1s with sulfuric acid of 30% to 65% concentration at a temperature between 150 F. and 220 F.,

and separating the resulting unsaturated dimer from the sulfuric acid. k 2. A process for producing the unsaturated dimer of an alpha alkyl styrene, which comprises intimately contacting said. alpha alkyl styrene with from 0.5 to 5 volumes of sulfuric acid-of 30% to 65% concentration at a temperature between 150 F. and 220 F., and separating the resulting unsaturated dimer from the sulfuric acid.

3. A process for producing .the unsaturated dimer of an alpha alkyi styrene, which comprises intimately contacting said alpha alkyl styrene with sulfuric acid of 50% to 65% concentration at a temperature between 60 F. and 220 F., -,and separating the resulting unsaturated dimer from the sulfuric acid.

go 4. A'processv for producing the unsaturated dimer of an alpha alkyl styrene, which comprises intimately contacting said alpha lkyl styrene with from 0.5 to 5 volumes of sulfuric acid of 50% to 65% concentration at a tem- 5 perature between 60 F. and 220 F., and separating the resulting unsaturated dimer from the sulfuric acid.

5. A process for producing the unsaturated dimer of alpha methyl styrene, which comprises so intimately contacting said alpha methyl styrene with sulfuric acidof to 65% concentration at a temperature between 150 F. and 220 F., and separating the resultingunsaturated dimer from the sulfuric acid.

6. A process for producing the unsaturated 40betee'1 .n22=r., the refractive index and bromine number. The w 50 F a d o and separating the intimately contacting said alpha ethyi' styrene with sulfuric acid of ranc ehtration at a temperature between 6 and,-.;2 20.F., and separating the resulting" un mer from the sulfuric acid. a

0 8. A process for producing unsaturated dimer of alpha methyl styrene, which comprises intimately contacting said alpha methyl styrene with from 0.5 to 5 volumes ofsulfuric acidof 50% to 65% concentration at a temperature between. F. and 220 F., and separatin'gthe resulting unsaturated dimer from the sulfuric acid. 9. A. process dimer of alpha methyl styrene, which comprises intimately contacting said alpha methyl: styrene with about 4 volumes sulfuric acid of 30%;to concentrationat adtemperature between 170 F. and 200 F., andseparatingthe resulting unsaturated dimer from the sulfuric acid.

10.. A process for producing the unsaturated dimer of alpha methyl styrene, which comprises intimately contacting said alpha methyl styrene with about 4 volumes of sulfuric acid of 50% to 65% concentration at a temperature betwe en F. and F., and separating-$13!} resulting unsaturated dimer from the sulfuric acid.

ARTHUR B, HERSBERGER. RANDALL G. HEILIGMANN.

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